It is officially set in the calibration regulations for the public domain. It determines the exact content of a glass by pressing in calibration bubbles in the glass. The state calibration office for glass vessels is located in Wertheim am Main, Germany.


Cold painting:
Decoration of glasses with varnish or oil-based paints. The Paints have not burned in or melted down.


Continous tank:
They are used for the production of flat glass, are 10 - 40 ms long and 3 - 6 ms wide.


Cooling crack:
A hidden glass defect which mostly appears after the production. The reason is the tension resulting from the cooling process. The cooling crack is recognizable in a flat running crack.


Cooling down:
That is a procedure to cool down glass products immediately after the production and to relieve tensions using a lehr.


Cooling process:
In the course of the moulding is a cooling process necessary to release the tensions building up in the glowing glass mass. This process takes place in a lehr. The duration of the cooling depends on the size of the products that has to be cooled.


The places which should not be grasped at the surface treatment. They are covered by elastic stencils or by suitable protective lacquer.


Crackle glass:
This refinement method has been used for glass produce modeled on crackle glazes for ceramics. The glass surface is covering with fine cracks and result in striking decorations. The cracks arise form quenching and they are closed by subsequent reheating but remain visible.


Crystal glass:
A high-quality, colourless, bubble-free and free of streaks glass that is characterised i.a. by especially high brilliance. In the table of the crystal glass identification law it is per- formed which ingredients the composition of the glass has to contain to be called crystal glass.


Cut iron:
A tool which is formed hook-shaped and is made of iron. It is used for cracking or rather separating flat and hollow glasses.